A while back I discovered that Pidgin is now available for Mac. The problem is that it is still a GTK app.
For Mac users that means it runs in X11. It has always bothered me that all X11 applications you run on Mac look so extremely ugly.
When I used Ubuntu a few years back I discovered mac4lin, a funny project that intends to make a Mac theme for Gnome.
Ironically, since Gnome is based on GTK you can run mac4lin on the system it intends to emulate, which would give your GTK apps a nice Mac look. Let's see how...
For this example I'm also going to install Pidgin, to show you how it looks.
First, however we need to get a bunch of software. You need to have MacPorts installed for this to work.

First we need to get GTK without X11. You can leave of the variants if the build fails to get the X11 version.

sudo port install gtk2 +quartz +no_x11

Now we can get Pidgin, or any other GTK2 app.

sudo port install pidgin +quartz +no_x11

To be able to easily switch theme later we also need this little app.

sudo port install gtk2-chtheme

Now download and extract the latest version of mac4lin from their website.

Extract Mac4Lin_GTK_Aqua_v1.0.tar.gz in the GTK folder to /opt/local/share/themes/ (You'll need to authenticate)

Run /opt/local/bin/gtk2-chtheme, select the newly installed theme.

Click the font button and set it to Lucida Grande at 10pt, done!

Run /opt/local/bin/pidgin to see the effect.

Before:
After:
Keyboard shortcuts: You might also want to use this hint to enable the CMD key for keyboard shortcuts.
Sound: By default Pidgin uses you 'system beep' to notify you, solution: